1. Field of the Invention
The present invention relates to a biaxial actuator adapted for use in a pickup device of a compact disc player or the like.
2. Description of the Background art
FIG. 3 shows an exemplary structure of a conventional biaxial actuator employed in an optical pickup device. In this known example, a cavity 2 is formed in a bobbin 1 of synthetic resin or the like for housing an objective lens 3 therein. And substantially rectangular recesses 4L, 4R are formed on both sides of the bobbin 1 so as to house focusing coils 5L, 5R therein respectively. Tracking coils 6L, 7L or 6R, 7R are bonded to the outer surface of the focusing coil 5L or 5R (on the reverse side with respect to the bobbin 1) by the use of a binder or the like. Each of the focusing coils 5L, 5R and the tracking coils 6L, 7L, 6R, 7R is shaped to be bobbinless.
Magnets 8L, 8R are disposed opposite to each other at positions outside the tracking coils 6L, 7L and 6R, 7R respectively. The magnets 8L, 8R are bonded respectively to the inner walls of outer bent portions of substantially U-shaped yokes 9L, 9R. And the inner bent portions of the yokes 9L, 9R are inserted respectively into hollows of the focusing coils 5L, 5R.
Therefore a magnetic flux generated from the magnet 8L is supplied to the inner bent portion of the yoke 9L via the inner vertical portions of the tracking coils 6L, 7L and the outer portions of the focusing coil 5L. This magnetic flux is fed back via the horizontal coupling portion of the yoke 9L to the outer bent portion thereof and further to the magnet 8L. Similarly, a magnetic flux generated from the magnet 8R is applied via the tracking coils 6R, 7R and the focusing coil 5R to the inner bent portion of the yoke 9R and then is fed back via the horizontal coupling portion of the yoke 9R to the outer bent portion thereof and further to the magnet 8R.
Consequently, when a focusing error signal is supplied to the focusing coils 5L, 5R, the bobbin 1 is driven in the focusing direction (vertically in the diagram). Meanwhile when a tracking error signal is supplied to the tracking coils 6L, 7L, 6R, 7R, the bobbin 1 is driven in the tracking direction (horizontally in the diagram). Thus a laser light beam incident on an unshown compact disc or the like via the objective lens 3 can be controlled in both focusing and tracking directions.
FIG. 4 typically illustrates the positional relationship between the magnet and the tracking coil in the known example of FIG. 3. In this example, the magnet 8R and the tracking coil 6R (or 7R) are disposed in parallel with each other. Such positional relationship is maintained also with regard to the magnet 8L and the tracking coil 6L (or 7L).
FIG. 5 shows another conventional example, wherein a focusing coil 23 is wound horizontally around a bobbin 21, and an objective lens 22 is incorporated therein. Tracking coils 24A, 24B wound to be bobbinless in advance are prepared for the bobbin 21 around which the focusing coil 23 is wound as mentioned, and hollow portions are fitted to the bobbin 21 and are bonded thereto fixedly, whereby the focusing coil 23 and the tracking coils 24A, 24B are disposed opposite to the left and right magnets 25L and 25R, respectively.
It is impossible, in this conventional example, to set a yoke in the bobbin 21, so that magnetic fluxes generated from the magnets 25L, 25R are not fed back.
In this example also, the bobbin 21 can be driven in both focusing and tracking directions by supplying a focusing error signal or a tracking error signal to the focusing coil 23 or the tracking coils 24A, 24B.
FIG. 6 typically illustrates the positional relationship between the magnet and the tracking coil in the known example of FIG. 5. In this example, the magnet 25R (and 25L) and the tracking coils 24A, 24B are so disposed as to be orthogonal to each other.
As described above, in the conventional biaxial actuator where the tracking coils 6L, 7L, 6R, 7R, 7R, 24A, 24B are wound to be bobbinless and then are bonded to the focusing coils 5L, 5R or the bobbin 21, many assembling steps need to be executed to consequently raise a problem of increase in the production cost. Furthermore, due to the bobbinless winding, it is necessary to use a self-welding wire as a coil wire with the requirement of ensuring a space for the binder, hence lowering the electromagnetic conversion efficiency. In addition, because of the bobbinless structure, a wire terminating process is not executable for the individual coil to eventually induce some difficulties in realizing automated manufacture.